How damp is your garage?
Mine is reasonably bad and I, as above, I mostly only get mould on the GS if I park it inside with a lot of dead bugs on the screen. But it cleans up well.
The HP2 lives under a breathable dust cover next to the drier wall (expanded clay bricks) and so far I've only had a tiny bit of mould over the seat when I uncovered the bike after winter, cleaned up well fairly quickly. I now tend to clean it a bit better when I recover it at the end of the warm season.
I have a DRZ that lives propped against a red brick wall (that seeps water if it rains a lot) on the opposite side and it's permanently covered in dirt. So far only a tiny bit of mould on the tail pack.